How To Do A Compression Check?

[BigMo82]

Was thinking of doing a cylinder compression test on my petrol avensis. I've never done this before but have always wanted to give it a shot.

My understanding is I take the engine cover off, then the coil pack is removed and then the spark plugs. The compression gauge with the correct fitting is then screwed into the spark plug sockets and then the ignition key is turned and I let the engine try to kick over for a few seconds and take the reading. I then follow this step for each of the cylinders.

My question is that I have read somewhere that if the throttle body is electronic then it must be kept open and I'm not sure if that's the case with the avensis and if it is then how can it be kept open?

Mo

[cooper12000]

never heard anything about an electronic throttle body.

u have the basic idea right. just make sure u take all the plugs out dont just do one at a time. it helps to have two people one to look at the gague and one to crank the engine over with the key. reason for this is u can watch how the needle moves... its all very well getting a final reading but how u get to that reading can be just as informative. u should get a couple of big jumps followed by 2-3 smaller ones untill the needle settles dont keep winding the engine once the needle has settled. and DO NOT put oil down the plug holes if u have a weak reading on one pot.

what r u hoping to achive by this.... do u hve an issue or doing just to try it???

hope this helps

coop

[+robster+]

Vw and mitsi probably more have a function in the diagnostics to open the stepper motor for the rhrottle wide open

Just as on a conventional throttle body you have to do this test at wide open throttle to let the air through without restriction and a fully charged Battery

Helps if the starter motor is in good condition too

You can do a cold , and hot test engine warm

Depends what the service manual gives you info on

[cooper12000]

thanks robster i hve learnt somthing there i didnt know about the electronic throttles thanks:)

[+robster+]

No probs

Ill take a pic of a fly by wite throttle body on one of our forklifts later today

[BigMo82]

Thanks for the replies gents. I haven't got any major issues but thought I would try it. I've got the pressure gauge and its only an hours worth of messing around at tops. Also still need to sort out that damn lambda sensor.

Mo

[jumbojake]

make sure you pull the fuse to the fuel pump (assume the petrol has electric fuel pump) .... last thing you want is a pile of un-burnt fuel fumes going down the exhaust pipe

I agree with Cooper ... if you can't see the gauge when turning the key, have someone else turn the key. You want to see a a good surge on the first stroke, then smaller 'pump' to a reliable reading.

The best cause of action on a modern engine is to check the ECU first... it should give you better indications of any miss-fire info ... it can sense the lack of acceleration on the crankshaft for each stroke, plus much more..

What's the problem you are trying to diagnose..??. IMO, mechanical faults (especially with Jap cars) is less likely than fuel or electic problems ....

[+robster+]

Good point some of our machines bring up a camshaft sensor fault when there is an imbalance. Sometimes not even noticable to the trained ear cause it trys to compensate and smooth things out

below hopefully the pic i promised

[BigMo82]

Thanks for the replies. Robster in not sure what I'm looking at in that photo? I'm not experienced with engines and can just about work my way around the easier to remove parts. So am I right in thinking all I have to do is remove the fuse to the fuel pump, all the sparks and screw in the pressure gauge? I can get a mate to key the ignition while I read the gauge.